Method of blasting



Patented Aug. 3, 1954 UNITED STATES PATENT OFFICE METHOD OF BLASTINGOriginal application December 17, 1947, Serial No. 792,202. Divided andthis application May 27, 1949, Serial No. 95,686

4 Claims.

This invention relates to a novel method of blasting under fluidconfinement and more particularly to a novel method of submarineblasting.

This application is a division of our co-pending application, Serial No.'7 92,202, filed December 17, 1947, now abandoned.

Underwater blasting operations are required for such purposes as thedeepening of harbors and channels, the removal of rock obstructions, thedestruction of sunken objects, and the like. In such work, it iscustomary to prepare the required number of boreholes spaced at suitabledistances apart and to load high strength explosive into each of saidboreholes. Heretofore in such blasting, it has been necessary to followone of two procedures, each of which involved serious disadvantages. Onemethod consisted in spacing the boreholes sufliciently close together,loading each of the holes with explosive, initiating one of the chargesby means of an electric blasting cap, and bringing about explosion ofthe other charges by propagation from hole to to hole. The disadvantageof such a method was that the use of explosives of a high degree ofsensitivity was required. As a matter of fact, it has been customary insuch work to employ 60% straight dynamite, high strength gelatin, orhigh strength gelatin primed with 60% straight. The use of highexplosives of such an order of sensitiveness is undesirable and undulyhazardous for large scale rock blasting operations where a certainamount of rough handling is necessary. Furthermore, premature explosionson drill barges with consequent loss of life have occurred with thesehighly sensitive explosives.

A second method practiced heretofore has allowed the use of many typesof cap-sensitive explosives but has necessitated the insertion of atleast one electric blasting cap into each borehole charge. This has notonly been wasteful in its requirements of relatively expensive electricblasting caps but has introduced complications because of the presenceof the many cap wires of considerable length, which could readily becometangled or fouled by material floating on or submerged in the water,nearby vessels, etc. A distinct hazard is involved also in the event ofelectrical storms, not necessarily in the immediate vicinity, which in anumber of cases have brought about the explosion of underwater chargeswith emergent cap wires.

In view of the disadvantages present in previous procedures forsubmarine blasting, where a plurality of explosive charges is to befired, it will be apparent that a method that allows the use ofrelatively insensitive explosives without requiring electric blastingcaps leading to each charge will represent a highly desirable advance.

An object of the present invention is a novel method of carrying outblasting operations beneath the surface of or in contact with a densefluid medium and particularly for underwater blasting. A further objectis such a method permitting the employment of relatively insensitiveblasting explosives and not requiring electric blasting caps and theirwires for the various charges. A still further object is a method forsubmarine blasting employing a novel type of detonator. Additionalobjects will be disclosed as the invention is described at greaterlength hereinafter.

We have found that the foregoing objects are accomplished when we carryout submarine blasting operations by a method comprising introducing aplurality of detonating explosive charges into the desired subsurfaceblasting positions; locating at least one blasting cap adjacent to eachof the explosive charges and in detonating relationship therewith, saidblasting cap being free from electrical firing arrangements and adaptedto become initiated under the efiect of pressure from the explosion of anearby charge; locating an explosive priming charge in suitableproximity to said blasting cap; bringing about the explosion of saidpriming charge; and thereby causing the collapse of the shells of theblasting caps, the initiation of the respective cap charges and thedetonation of the main explosive charges adjacent thereto. Thedetonators or blasting caps adapted to become initiated under the efiectof pressure, as described, may, for example, contain loosely-packedcharges of impactignitible mixtures within a portion of the shell, whichbecome fired as a result of the impact of the collapsing walls. The highvelocity compressed detonating explosive base charge within the cap willbe brought to explosion by the loose charge. A blasting cap of the abovecharacteristics and structure is fully disclosed and claimed in ourco-pending application, Serial No. 792,202.

The invention will be illustrated more clearly by reference to theattached drawing, in which Figures 1, 2 and 3 are diagrammatic views ofdifferent arrangements of explosive charges under water, adapted toemploy the principle of the invention.

In Figures 2 is shown an assembly for underwater blasting using apressure-responsive detonator. In this figure, Ill represents thesurface of a body of water, beneath which, and confined by said body,have been placed explosive charges I? and I3, in boreholes in the rockbottom. Inserted in these charges are pressure responsive blasting capsl4 and I5. An explosive charge I6 has been lowered into a position inproximity to caps M and I5, and an electric blasting cap I? is indetonating relationship with this charge, having insulated cap wires l8.When ready for the blast, the cap wires are thrown into circuit with asource of electric current (not shown) and the charge is fired. Thepressure resulting from the detonation of charge l6 brings about theinitiation of caps 14 and 5, with consequent detonation of the charges[2 and [3. In this figure, two explosive charges have been showncontaining inserted propagation detonators and in position to beexploded under the influence of pressure.

Figure 1 shows another and a preferred assembly of charges forunderwater blasting employing the pressure-responsive detonator. In thisfigure, six explosive charges IS-M, are shown loaded into theirrespective boreholes in the rock bottom, spaced from one another atreasonably short distances. Into charge i9, an electric blasting cap 25has been inserted, having insulated cap wires 36. Spaced from charge l9are the successive explosive charges 20, 2!, 22, 23 and 24, into each ofwhich has been introduced a nonelectric closed detonator of the typedescribed, these detonators being designated by 26, 2'1, 28, 29 and 39respectively. At the time of firing, the wires from the cap in explosivecharge is are connected with a source of firing current and electricblasting cap 25 and charge 19 are brought to detonation. The adjacentexplosive charges 2fi24 are not sufficiently sensitive to propagation tobe detonated sympathetically from the first charge 49, but the resultingpressure causes the collapse of the walls of cap 26 and the detonationof this and its charge 26 and the subsequent successive detonation ofcharges 2 l24 by means of the inserted pressure-sensitive detonators. Itwill be understood that, in the illustration of the invention accordingto Figure 2, the explosive charges in the different boreholes mayconsist of single cartridges in each hole or a column or group ofcartridges. Where a number of cartridges are present in each hole, asingle pressure responsive detonator in the top cartridge may besuificient, the explosion propagating from one cartridge to another, or,if desired, propagation detonators may be present in all or in anychosen number of the cartridges, depending on the sensitiveness of theexplosive and the continuity of the column.

Figure 3 illustrates a vertical sprung hole where chambering is desired.The small diameter vertical borehole 3? opens into the enlarged chamber38, which is filled with water to the level 39. Into this hole have beencharged a great number of explosive cartridges or cans, as shown. Apriming cartridge 40 contains an inserted electric blasting cap H, theleading wires 42 from which pass up outside the hole. Propagationdetonators may be inserted into all or as many of the cartridges asdesired. The priming cartridge is fired by connecting the blasting capwires to a source of electric current and the presence of propagationdetonators, adapted to fire under the action of the pressure from thepriming cartridge, assures complete detonation of all cartridges and theconsequent desired enlargement of the chamber.

The method described in the foregoing will be applicable in blastingoperations beneath the surface of a dense fluid medium, and particularlyin submarine blasting, for the deepening of harbors and channels, theremoval of rock obstructions, the destruction and disintegration ofsunken objects, shaft sinking, and the like. It has other sub-fluidapplications, however, for example in oil well shooting and in varioususes of explosives in the oil production industry. By the words densefluid medium we intend to in clude all liquids and fiowable solids suchas mud, wet sand and all solid-containing mixtures that may be caused tofiow under pressure. The method is applicable, for example, in ditchblasting where the explosion is propagated from cartridge to cartridgeby sympathetic detonation through a wet soil medium.

The method of underwater blasting according to the present invention isoutstanding in its advantages. The pressure-responsive detonators usedare simpler in design and more economical in cost of materials thanelectric blasing caps. Since only one electric blasting cap is requiredfor a group of shots, this means a very considerable saving,particularly in cap wires and electrical firing means. At the same timethe disadvantages are avoided of a large number of sets of cap wiresthat may become fouled by floating or submerged objects and mayconstitute a hazard during the occurrence of electrical storms, even ata considerable distance from the place of blasting.

A particular advantage comes from the fact that the method allows thesatisfactory and effective use of explosives of a lower order ofsensitivity than has been possible heretofore in the usual proceduresfollowed. It has previously been the practice in submarine blasting toemploy 60% straight dynamite, in order to assure complete detonationwhere propagation from hole to hole was desired. This 60% straightdynamite is of a high order of sensitivity and its use in large scaleblasting operations is not desirable because of the rough treatmentinvolved and the care required in such handling. Using the method of thepresent invention, any cap sensitive explosive may be employed and wefind highly desirable explosives relatively insensitive to impact suchas those high in ammonium nitrate content, for instance over 60%ammonium nitrate, non-nitroglycerin explosives containing solidsensitizers, granulated cast mixtures of ammonium nitrate andtrinitroltoluene; blasting agents of the Nitramon type where acap-sensitive booster charge is required, and many others. With suchexplosives, having a pressureresponsive detonator inserted in eachcartridge or in each group of cartridges, the advantages are obtained ofexcellent blasting execution, simplicity of assembly, and freedom fromthe hazards sensitive explosives. It will be understood that, when theterm explosive charge is used, this may designate either a singleexplosive cartridge or a group of cartridges in substantial contact orin detonating relationship with one another.

The invention has been disclosed at length in the foregoing but it willbe understood that many changes in details of charges, arrangement ofcharges, assembly and detonator design may be made without departurefrom the scope of the invention.

We intend to be limited, therefore, only by by the following claims.

We claim:

1. A method of blasting beneath the surface of a dense fluid medium,which comprises introducing into each of a plurality of desiredsubsurface blasting positions at least one relatively insensitiveexplosive charge at such a distance from other said positions thatsympathetioal detonation by other charges in said other positions isprecluded; locating at least one pressure ignitable detonator indetonating relationship with said charges; placing an explosive primingcharge in proximity to said detonators; bringing about the explosion ofsaid priming charge; and thereby causing pressure-induced ignition ofthe said detonators, the initiation of the respective detonator charges,and the detonation of the explosive charges.

2. The method of claim 1, in which the charges of detonating explosivecomprise compositions high in ammonium nitrate content.

3. The method of claim 1, in which the charges of detonating explosivecomprise mixtures of ammonium nitrate and trinitrotoluene.

4. The method of claim 1, in which the charges of detonating explosivecomprise relatively insensitive ammonium nitrate compositions, saidcompositions being adjacent to booster charges of ca -sensitivematerial.

References Cited in the file of this patent UNITED STATES PATENTS 166 ofthe Du Pont Blasters Handbook, 1939 (cited in the preceding action) isadded to the record.

Explosives, by Martin Meyer, published by Thomas Y. Crowell 00., N. Y.1943, pp. 291, 292. 294, 295, 296. Copy in Scientific Library.

1. A METHOD OF BLASTING BENEATH THE SURFACE OF A DENSE FLUID MEDIUM,WHICH COMPRISES INTRODUCING INTO EACH OF A PLURALITY OF DESIREDSUBSURFACE BLASTING POSITIONS AT LEAST ONE RELATIVELY INSENSITIVEEXPLOSIVE CHARGE AT SUCH A DISTANCE FROM OTHER SAID POSITIONS THATSYMPATHETICAL DETONATION BY OTHER CHARGES IN SAID OTHER POSITIONS ISPRECLUDED; LOCATING AT LEAST ONE PRESSURE IGNITABLE DETONATOR INDETONATING RELATIONSHIP WITH SAID CHARGES; PLACING AN EXPLOSIVE PRIMINGCHARGE IN PROXIMITY TO SAID DETONATORS; BRINGING ABOUT THE EXPLOSION OFSAID PRIMING CHARGE; AND THEREBY CAUSING PRESSURE-INDUCED IGNITION OFTHE SAID DETONATORS, THE INITIATION OF THE RESPECTIVE DETONATOR CHARGES,AND THE DETONATION OF THE EXPLOSIVE CHARGES.